Tube heater



Jan. 2, 1968' F. o. HESS 3,361,538

TUBE HEATER Filed Nov. l5, 1964 INT/M7012 FREDERIC O. HESS ATTORN EY United States Patent O 3,361,538 TUBE HEATER Frederic 0. Hess, Skytop, Pa., assignor to Selas Corporation of America, a corporation of Pennsylvania Filed Nov. 13, 1964, Ser. No. 411,074 8 Claims. (Cl. 23--284) The present invention relates to furnaces, and more particularly to that type of furnace known as a tube heater for heating uids in the chemical and petrochemical industries.

Usual heaters of the type with which this invention'is concerned are provided with one or more elongated serpentine tubes that extend through a convection section and a radiant section of the heater. It is important to be able to control the temperature of the tube, and the uid flowing through it, accurately at various points along its length. One of the most critical points of control of temperature is the transition between the convection section arid the radiant section where the uid is suddently subjected to high reaction temperatures.

The severe heating to which the tubes are subjected requires that they be inspected frequently in order that they can be replaced, if necessary, before failure. This has been a diilcult and time consuming task.

It is an object of the invention to provide a furnace structure which makes it possible to control accurately the temperature of the tube in various portions of the furnace, and particularly at the cross-over point between the convection and radiant sections.

It is a further object of the invention to provide a tube heater in which the radiant section of the tube may be easily and quickly removed for inspection and repair of the tube and the tube supports.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specication. For a better understanding of the invention, however, its advantages and specific objects attained with its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

In the drawings:

FIG. 1 is a section through the furnace,

FIG. 2 is a section taken on line 2 2 of FIG. 1, and

FIG. 3 is a section of a modified form of the invention.

The furnace is built in accordance with ordinary furnace practice of refractory material that is backed up by sheet metal. The furnace consists of a pair of parallel side walls 1 and 2 and an end wall between them that are supported in a conventional manner by buck-stays 3 to form an elongated radiant chamber 4. The furnace walls extend upwardly at 5 and 6, which walls are supported by buck-stays 7 to form an upper convection chamber 8. Above this chamber the exhaust gases are discharged through one or more stacks 9.

The chambers are relatively long in a plane perpendicular to the drawing and relatively narrow and are rectangular in shape. One end of the chamber will be closed by an end wall, as noted, while in this case the other end is closed, as shown in FIG. 2, by a pair of doors 11 that are hinged at 12 to the side walls 1 and 2. These doors are normally maintained closed but can be opened `so that the entire end of the furnace is open for a purpose to be described below.

The lower portions of walls 1 and 2 extend inwardly toward the center of the furnace to cooperate with a floor 13 that is separate from the walls. The floor is rigidly constructed and is mounted on suitable beams 14 that are in turn supported by a plurality of jacks 15 on a carriage 16. The carriage is mounted on wheels 17 that travel on tracks 18 which are parallel to the side walls of the furnace and extend beyond the end of the furnace having doors 11.

Floor 13 has attached to it. extending upwardly, a plurality of tube supports 19 which serve to support the passes of a serpentine tube 21 which forms the coil section in the radiant section of the heater. This coil is heated by a plurality of horizontal rows of burners 22 that are placed in the side walls 1 and 2 of the furnace and are directed toward the coil with separate rows of burners being directed primarily toward separate passes of the coil. The upper end of coil 21 is connected by a conventional joint with the lower end of a serpentine coil 23 forming the convection coil section that is located in chamber 8 of the heater. While the two coils 21 and 23 are located in different sections of the heater, they are connected and actually form a continuous tube through which fluid flows as it is being progressively heated.

The radiant chamber and the convection chamber 8 are separated by a radiation shield 24 that is provided with a plurality of openings 25 through which products of combustion can pass. This shield can have various shapes and serves the purpose of blocking substantially all of the direct radiant heat from the higher temperature radiant chamber 4, so that the upper chamber 8 will be heated only by convection from the hot gases passing through openings 25. Temperature of the gases passing through the convection chamber 8 can be changed by means of products of combustion from a series of burners 26 and by air introduced through inlets 27 that extend along the walls 5 and 6. As indicated in the drawings, the burners and the air inlets alternate along the wall and in opposite walls a burner is opposed by an air -inlet 27.

In the normal construction of a tube heater of the type with which this invention is concerned, the iiuid to be heated is introduced into the convection coil section which extends back and forth along the length of the upper furnace chamber in a plurality of passes that are connected by U-bends. The tube then goes through a suitable connection to the radiant coil section 21 which also passes back and forth through the lower furnace chamber with each of the passes of this portion of the tube being connected by a U-bend. In operation, the material in the tube to be heated passes through the convection coil section 23 where its temperature is brought up to some value slightly below the reaction temperature. The fluid then passes into the radiant coil section 21 where it is rapidly heated under severe conditions to bring it quickly to the reaction temperature to perform the reaction desired.

The radiant section of the heater is heated by burners 22 which are preferably of the type disclosed in Williams et al. Patent No. 3,076,498. These burners heat the walls of the furnace to incandescence and direct radiant heat toward the tube passes in front of them, somewhat in the manner of search lights. Therefore, by firing the different horizontal rows of burners at different rates, normally intense radiant heat can be directed at various specific tube passes to control the temperature of each group of passes of the tube to various degrees and thereby control the temperature gradiant of the liquid flowing through the tube. Some heat is also produced, of course, by the hot products of combustion from the burners. These products of combustion ow upwardly through the furnace chamber and through openings 25 in shield 24 to heat the convection section 23 of the tube before the gases are exhausted through the stack. In many chemical reaceions it is necessary to preheat the Huid being treated to a given value below the reaction temperature and then increase the temperature of the Huid rapidly and severely. The cross-over temperature, or the temperature of the fluid as it passes from the convection to the radiant section of the coil, is in many cases critical. For this reason, it is necessary to control accuthe required amounts through inlets 27. If, on the other hand, additional heat is needed in the convection section above that which is normally obtained by gases passing through openings 25, burners 26 can be used to supply products of combustion to heat these gases. It will be noted that burners 26 and air inlets 27 are so disposed along the length of the chamber that the temperature of the gases passing through chamber 8 can be evenly regulated to the same value from one end of the chamber to the other.

In the modern pyrolysis of hydrocarbons thetemperature and pressure conditions are severe so that it is necessary frequently to inspect the tubes in order to determine when they should be replaced. This has normally been a ditiicult job because of the length of the tubes and the relatively narrow space between the tubes and the burners. With the present invention, however, when inspection is required, it is only necessary to open doors 11 and lower floor 13 by means of jacks 15. Then, by breaking the connection in the tube between the convection and radiant sections, the entire oor carrying the tube supports and the radiant section of the tube, can be moved out of the furnace into the open air and it can be inspected easily, .and sections of the tube can be replaced if necessary. It is not necessary to wait until the entire heater has cooled down. This is a particularly advantageous arrangement where fragile tubes are being used since the tubes are not moved on their supports. To return the furnace to operation, it is only necessary to move the car so that the floor is relocated between the furnace walls, elevate the floor by jacks 15 and close doors 11. Naturally, the tube sections between the radiant and convection sections will be connected. For this purpose a standard pipe fitting of a suitable material can be used.

FIG. 3 shows another form that the invention can take. In this embodiment, the radiation shield instead of being generally in the form of a bridge wall, comprises shoulders 2S and 29 that project from the side walls toward the center of the heater lbetween the radiant and convection sections. A gap 31 extends the length of the furnace between the shoulders for the passage of combustion gases from chamber 4 to chamber 8. This gap is directly above the tube support and coil and is therefore vlocated so that practically no direct radiation from the walls of the lower chamber passes to the upper coil. As the products of combustion pass through gap 31 into chamber 8 their temperature can be adjusted by burners 26 or air from inlets 27. Thus with this construction, as with that of FIG. 1, the convection heating of coil section 23 can be accurately controlled.

From the above, it will be seen that I have provided a furnace in which each section of the coil can be heated exactly to the desired temperature and that various passes of the radiant section of the coil can be heated to this temperature if necessary or desirable. The furnace is also so constructed that the entire radiant section of the tube can be easily moved for inspection and repair.

While in accordance with the provisions of the Statutes I have illustrated and described the best form of embodiment of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit and scope of the invention set forth in the appended claims, and that in some cases certain features of my invention may be used to advantage Without a corresponding use of other features.

What is claimed is:

1. A tube heater comprising in combination structure including side walls to form an elongated narrow rst furnace chamber, rows of burners extending horizontally in said side walls, additional structure forming a second chamber having side walls located above said rst chamber, a row of burners in each of said last mentioned side Walls, radiation retarding means between said two chambers operative substantially to prevent radiation of heat from said rst chamber to said second chamber, said means being provided with an opening substantialiy smaller in area than said chambers through which products of combustion from said first chamber can flow to said second chamber, and a tube midway between said side walls of said first chamber through which fluid to be heated ows, said tube having a portion thereof located in said second chamber, said portion to beA heated by products of combustion owing through said opening.

2. A tube heater comprising in combination structure forming the sides and one end wall of a rectangularrfurnace chamber, door means closing the other end of said chamber, a floor for said chamber received between said sides, a tube support extending upwardly from said iloor into said chamber, a tube carried by said support, tracks extending under said structure, a car mounted for movement on said tracks, and extensible means on said car to support said floor, whereby said floor can be raised into yposition between said sides or lowered and be moved with said car along said tracks to a :position beyond said chamber.

3. In a tube heater, the combination ofstructure forming an elongated, narrow, substantially rectangular furnace chamber having side walls and an open bottom, horizontal rows of burners in said side walls, a door closing the bottom of said chamber, a tube support extending upwardly from said floor into said chamber, a tube coil mounted on said support, tracks beneath the open bottom of said chamber and extending lengthwise thereof, a car movable on said tracks, and extensible means on said car to support said floor in position to close the bottom of said chamber, whereby upon contraction of said extensible means said oor can be lowered and moved with said car away from said structure.

4. A tube heater comprising in combination structure forming ya first chamber having opposite sides and a floor, rows of burners in said sides to heat said chamber directly from heat produced by said burners, structure forming a second chamber above said first chamber, said second chamber also having opposite sides, means extending between said chambers substantially to prevent radiant heat produced by said first chamber from heating said second chamber, said means being provided with an opening substantially smaller in area than said chambers through which products of combustion can pass from said rst to said second chamber, a continuous tube midway between the sides of said chambers having a portion thereof in each of said chambers, and means in the structure forming said second chamber to change the temperature of the products of combustion flowing Vthrough said opening from said first chamber to said second.

5. The combination of claim 4 in which said means in said structure includes a plurality of burners discharging products of combustion into said second chamber and a plurality of inlet ports through which air can be discharged into said second chamber.

6. In a tube heater, the combination of structure forming an elongated radiant heating chamber and a superposed convection heating chamber, each having siderand end walls and an opening in the bottom of Vsaid radiant chamber, radiation shield means between said chambers, said shield means being provided with an opening therein, a plurality of burners in the side Walls ofV said radiant chamber to supply heat thereto, the products of combustion from said burners pas-sing through said opening to said convection chamber, means in the side walls of said convection chamber to change the temperature of the gases flowing thereto, "a oor to fit the opening in the bottom of said radiant chamber, a car arranged for movement from a location beneath said furnace structure to a location beyond one end thereof, means to mount said floor on said car, a tubular coil having a portion thereof in said convection chamber and a portion thereof in said radiant chamber, and means to mount the portion of s-aid coil in said radiant chamber on said Hoor, one end wall of said chamber being movable whereby said coil portion mounted on said oor can be moved out of the chamber as said car is moved.

7. A tube heater comprising in combination structure forming an elongated furnace chamber having a pair of vertically extending and parallel side walls, said chamber being rectangular in shape with said side Walls forming the long sides of the rectangle, a plurality of horizontal rows of burners in each of said side Walls7 a shoulder projecting from each side Wall adjacent to the top of said chamber, said shoulders approaching each other and leaving between them an elongated gap substantially narrower than said chamber through which products of combustion from said burners will pass, means forming a second chamber above said rst mentioned chamber, said second chamber also being rectangular in shape and of substantially the same area as said iirst mentioned chamber, a row of burners in each of the portions of said means above said side walls, a rst serpentine tube coil in said first mentioned chamber, said coil including horizontally extending tube portions substantially midway between said side walls and a second coil connected to said first coil, said second coil being loc-ated in said second chamber between said rows of burners in said second chamber.

8. A tube heater comprising in combination means forming an elongated, vertically extending furnace chamber that is rectangular in shape, said means including a pair of oppositely disposed, parallel side Walls, a shoulder projecting from the top of each wall toward the other with a gap substantially narrower than said chamber left between said shoulders, said gap extending substantially the length of said furnace chamber, means forming ya second chamber above said iirst mentioned chamber, said last means including second parallel walls on top of said first walls, a plurality of horizontally extending rows of burners opposing each other in said first mentioned walls, a row of horizontally extending rows of burners in each of said second parallel walls, said shoulders being located to prevent substantially the radiation of heat from said first mentioned chamber to said second chamber, a tube coil having a portion thereof in said iirst mentioned chamber and a portion thereof in said second chamber, said portions being connected and being located substantially midway between said pairs of side walls, each coil portion having horizontally extending lengths of tube heated by the rows of burners adjacent thereto.

References Cited UNITED STATES PATENTS 1,166,422 1/ 1916 Armstrong 202-252 2,527,410 10/1950 Fleischer 122-356 2,716,968 9/1955 Hess et al 122-510 JAMES H. TAYMAN, JR., Primary Examiner. 

2. A TUBE HEATER COMPRISING IN COMBINATION STRUCTURE FORMING THE SIDES AND ONE END WAL OF A RECTANGULAR FURNACE CHAMBER, DOOR MEANS CLOSING THE OTHER END OF SAID CHAMBER, A FLOOR FOR SAID CHAMBER RECEIVED BETWEEN SAID SIDES, A TUBE SUPPORT EXTENDING UPWARDLY FROM SAID FLOOR INTO SAID CHAMBER, A TUBE CARRIED BY SAID SUPPORT, TRACKS EXTENDING UNDER SAID STRUCTURE, A CAR MOUNTED FOR MOVEMENT ON SAID TRACKS, AND EXTENSIBLE MEANS ON SAID CAR TO SUPPORT SAID FLOOR, WHEREBY SAID FLOOR CAN BE REAISED INTO POSITION BETWEEN SAID OR LOWERED AND BE MOVED 